“Lab-on-a-chip” (LOC) is a term describing devices of only a few square millimeters or centimeters, which are able to perform a myriad of tasks normally associated with a standard laboratory. LOC devices comprise microfluidic channels, which and are capable of handling very small fluid volumes in the nanoliter or picoliter range. The applicability of LOC devices for chemical and biological analysis has fuelled research in this field, especially if LOC devices can be fabricated cheaply enough to provide disposable biological analysis tools. For example, one of the goals of LOC technology is to provide real-time DNA detection devices, which can be used once and then disposed of.
Fabrication of LOC devices evolved from standard MEMS technology, whereby well-established photolithographic techniques are used for fabricating devices on silicon wafers. Fluidic control is crucial for most LOC devices. Accordingly, LOC devices typically comprise an array of individually controllable microfluidics devices, such as valves and pumps. Although LOC devices originally evolved from silicon-based MEMS technology, more recently there has been general shift towards soft lithography, which employs elastomeric materials. Elastomers are far more suitable than silicon for forming effective valve seals. Thus, polydimethylsiloxane (PDMS) has now become the material of choice for fabricating microfluidics devices in LOC chips. A PDMS microfluidics platform is typically fabricated using soft lithography and then mounted on a glass substrate.
One of the most common types of valve employed in LOC devices is the ‘Quake’ valve, as described in U.S. Pat. No. 7,258,774, the contents of which is incorporated herein by reference. The ‘Quake’ valve uses fluidic pressure (e.g. pneumatic pressure or hydraulic pressure) in a control channel to collapse a PDMS wall of an adjacent fluid flow channel, in the manner of a conventional pneumatic pinch valve. Referring briefly to FIGS. 1A-C, the Quake valve comprises a fluid flow channel 1 and control channel 2, which extends transversely across the fluid flow channel 1. A membrane 3 separates the channels 1 and 2. The channels 1 and 2 are defined in a flexible elastomeric substrate, such as PDMS, using soft lithography so as to provide a microfluidic structure 4. The microfluidic structure 4 is bonded to a planar substrate 5, such as a glass slide.
As shown in FIG. 1B, the fluid flow channel 1 is “open”. In FIG. 1C, pressurization of the control channel 2 (either by gas or liquid introduced therein by an external pump) causes the membrane 3 to deflect downwards, thereby pinching the fluid flow channel 1 and controlling a flow of fluid through the channel 1. Accordingly, by varying the pressure in control channel 2, a linearly actuable valving system is provided such that fluid flow channel 1 can be opened or closed by moving membrane 3 as desired. (For illustration purposes only, the fluid flow channel 1 in FIG. 1C is shown in a “mostly closed” position, rather than a “fully closed” position).
A plurality of Quake valves may cooperate to provide a peristaltic pump. Hence, the ‘Quake’ valving system has been used to create thousands of valves and pumps in one LOC device. As foreshadowed above, the number of potential chemical and biological applications of such devices is vast, ranging from fuel cells to DNA sequencers.
However, current microfluidics devices, such as those described in U.S. Pat. No. 7,258,774, suffer from a number of problems. In particular, these prior art microfluidics devices must be plugged into external control systems, air/vacuum systems and/or pumping systems in order to function. Whilst the microfluidics platform formed by soft lithography may be small and cheap to manufacture, the external support systems required to drive the microfluidics devices means that the resulting μTAS device is relatively expensive and much larger than the actual microfluidics platform. Hence, current technology is still unable to provide fully integrated, disposable LOC or μTAS devices. It would be desirable to provide a fully integrated LOC device, which does not require a plethora of external support systems to drive the device.